1. Field of the Invention
The present invention relates to a method of manufacturing a water disintegratable non-woven fabric easily dispersed by water streams and the water disintegratable non-woven fabric obtained by the method. More specifically, it relates to a method of manufacturing a bulky water disintegratable non-woven fabric having excellent water disintegratability and wet strength and to the water disintegratable non-woven fabric obtained by the method.
2. Description of Related Art
Cleaning sheets made of paper or non-woven fabric are used for wiping human skins such as of hips or for cleaning toilet articles. The cleaning sheets are preferably water disintegratable so that they can be thrown away to toilets after use. Because, when they are thrown away into a toilet, it would take much time to disperse them in a septic tank unless they are highly water disintegratable, and they possibly clog drainages of the toilets.
Disposable fibrous cleaning sheets to be used for wiping are usually marketed while being packaged in a state previously wetted with liquid cleaning medicals in view of convenience and handlability. Such cleaning sheets must have wet strength sufficient to endure wiping in a state impregnated with liquid cleaning medicals, and are required to be water disintegratable when thrown away to toilets.
As such cleaning sheets, Japanese Patent Publication Hei 7-24636, for example, discloses a water disintegratable cleaning article containing a water soluble binder having carboxyl groups, metal ions and an organic solvent. The cleaning article has predetermined strength upon use, and when it thrown away into toilets, it tends to be dispersed in water since the binder is dissolved. However, since the cleaning article has, generally speaking, a constitution of paper, the fiber density is high. Accordingly, it can not give a bulky or soft feeling.
On the other hand, Japanese Patent Unexamined Publication Hei 9-228214 discloses a water disintegratable non-woven fabric obtained by mixing fibers having a fiber length of from 4 to 20 mm and pulp and entangling them by a high pressure water jet stream treatment and having wet strength of from 100 to 800 gf/25 mm as measured according to JIS P 8135. Since this non-woven fabric is formed by entangling fibers, it has a bulky feeling. However, this non-woven fabric is formed by entangling fibers having a long fiber length by a high pressure water jet treatment to provide relatively high wet strength. Therefore it is difficult to attain bulkiness, strength and water disintegratability in good balance, so that this non-woven fabric is not suitable to be thrown away into flushing toilets.
An object of the present invention is to provide a water disintegratable non-woven fabric having satisfactory water disintegratability and high wet strength, as well as having a bulky and soft feeling.
Another object of the present invention is to provide a water disintegratable non-woven fabric having an excellent wiping effect.
The objects and advantages of the present invention are attainable by a method of manufacturing a water disintegratable non-woven fabric comprising:
a step of forming a fiber web from fibers having a fiber length of 10 mm or less,
a step of applying a water jet treatment to the fiber web to obtain a fiber sheet having wet strength of less than 100 g/25 mm in MD and CD, the wet strength being defined by tensile strength at break of the fiber sheet, as measured by using a tensilon tester with a chuck distance of 100 mm, at a tensile speed of 100 mm/min to the fiber sheet which is cut into 25 mm width and 150 mm length and impregnated with water in an amount 2.5 times the weight of the fiber sheet, and
a step of adding at least one binder selected from the group consisting of carboxymethyl cellulose, alkylcellulose, polyvinyl alcohol and modified polyvinyl alcohol to the fiber sheet, to obtain a water disintegratable non-woven fabric.
The present invention further provides a water disintegratable non-woven fabric, obtained by the method.
In the present invention, the fiber sheet is obtained to have predetermined wet strength by applying the water jet treatment to the fiber web. Then, the binder is added to the fiber sheet to obtain a water disintegratable non-woven fabric where wet strength is further enhanced. This non-woven fabric has high wet strength upon wiping, and can be readily disintegrated in water when it is brought into contact with a large quantity of water, because the binder is dissolved or swollen to release the bonding between the fibers.
In addition, the water disintegratable non-woven fabric of the present invention has a bulky soft feeling and an excellent wiping effect.
The basis weight of the fiber web is preferably from 20 to 100 g/m2.
The fiber preferably comprises pulp of conifer and rayon having a fiber length of 7 mm or less. In this case, preferably, the blending ratio of the pulp of conifer is 30% by weight or more and the blending ratio of the rayon is 70% by weight or less.
The fiber density of the fiber sheet is preferably 0.3 g/cm3 or less.
It is preferred that the work load of the water jet treatment per one processing is from 0.05 to 0.5 kW/m2 and the fiber web is processed with the water jet treatment from 2 to 4 times. In this case, the water jet treatment is preferably conducted by using nozzles having a diameter of from 90 to 100 xcexcm and aligned each at an interval of from 0.3 to 0.7 mm in CD.
The water disintegratability of the fiber sheet is preferably 100 sec or less as measured by a toilet paper disintegratability test according to JIS P 4501.
The content of the binder is preferably from 0.5 to 30 g based on 100 g of the fibers.
An aqueous solution in which an electrolyte selected from the group consisting of water soluble organic and inorganic salts is dissolved are preferably impregnated in the non-woven fabric, after the step of adding the binder.
The water disintegratable non-woven fabric of the present invention preferably has water disintegratability of 120 sec or less as measured by a toilet paper disintegratable test according to JIS P 4501.